Why Does Heating a Flask Change Its Weight?

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Heating a glass flask can lead to a slight decrease in its weight due to the expulsion of air and water vapor, which can escape as the temperature rises. The ideal gas law indicates that gas volume increases with temperature, potentially causing some gas to leave the flask if it’s not sealed. In a sealed vacuum flask, heating would not change the mass, as there are no gases to escape. The discussion highlights a common misconception regarding the relationship between temperature and mass in gases. Overall, the weight change is primarily related to the behavior of gases under heat rather than a direct loss of mass from the flask itself.
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If you heat up a glass flask why will the weight of the flask decrease slightly?

The lab we're doing deals with the ideal gas law, so maybe it has to do with the mass being inversely proportional to the temperature? Or is there another reason?

Also, what would happen if you heat up a flask with no air in it that's sealed off from the outside (so inside the flask is like a vacuum)? Would the mass decrease?
 
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What do you think? Why on Earth do you think the weight of the flask will decrease, even slightly? The ideal gas law doesn't say mass will decrease. It says the ratio of mass to volume will decrease under constant pressure.
 
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Thread 'Magnitude of buoyant force in fluids of different densities'

The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?
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